It all depends on the individual and the joint to be cooked. Personally, I love cooking a good Brisket slowly in some beef stock and red wine, You can cook it all day and gas mark 2-3 and it literally falls apart with a sharp knife.
I serve it with Fresh Carrots and a Cheesy/Garlic mash with Roasties. They complement the brisket beautifully.
I sometimes go for topside. I make a baste of butter fried shallots with the slightest hint of garlic. Small cup of beef stock and a glass of Shiraz. Again I slow cook this.
I am not a big fan of Beef that is covered in Mustard or other marinades.
@ OP, you could always roast the small spuds with a bit of Rosemary.